While not restricted thereto, this invention finds immediate application in simple, inexpensive power supplies and in simple, inexpensive battery charging circuits and the like. The battery charging circuits are especially useful for charging batteries used in portable battery-operated devices such as household appliances, soldering pencils, shavers, cordless telephones, calculators, computers, television sets, radios, recorders, electric garden tools, cordless hand tools including cleaning, woodworking and metalworking tools, and the like. The present invention also finds direct application in D.C. power supplies suitable for use in radios, recorders, shavers, calculators, computers, recorders, cleaning, woodworking and metalworking tools, household appliances, and the like.
Integrated circuit realizations of the present invention are simple, inexpensive to make and may be readily incorporated directly into the devices to be powered, into power cords and into plugs which are attached to power cords.
Battery-operated cordless devices and other battery-operated devices, such as hand tools, have considerable popularity because of the convenience afforded by these devices. Tools and appliances of this type are customarily provided with a small D.C. electric drive motor which is energized by one or more rechargeable batteries incorporated within the tool housing and operatively associated with the electric drive motor. When the device is a television set, radio, recorder or the like, the rechargeable batteries supply D.C. power to the circuits therein either exclusively or alternatively, in instances in which an A.C. power cord and plug are provided. The elimination of a conventional electric cord or its alternative use increases the freedom with which the user of the cordless device can move about, eliminating the inconveniences of clearing the power cord from obstacles with which it may otherwise become entangled and reducing the necessity of having electric wall outlets available at every place the device is to be used. It has become customary to provide cordless devices, such as cordless garden tools and woodworking tools with rechargeable batteries so as to avoid the necessity of frequent battery replacements, and to reduce the cost of operation. The present day rechargeable batteries, properly maintained with a special charge, have an extended life and greatly enhanced convenience with which the cordless device may be operated.
Most cordless devices, such as cordless hand tools and the like, operate from a D.C. battery potential of only a few volts.
It is known from U.S. Letters Pat. No. 3,943,423 to Philip A. Hoffman entitled "Battery Charging Circuit" and issued on Mar. 9, 1976 to provide a battery charging circuit which eliminates the need for a relatively bulky and heavy voltage step-down transformer, and which, when recharging batteries in a hand tool or the like, needs simply to be connected to a conventional, 117 volt 60 Hz. household outlet and to the battery, battery-pack cell or cells which are to be recharged. Other outlet voltage levels and/or supply frequencies can be used as well. The known charging circuit of the aforesaid Hoffman patent comprises a variable resistance switch preferably realized in the form of a NPN junction transistor and Darlington-connected other transistors, operatively associated with a feedback circuit. This known circuit produces current pulses which effect charging of a battery or battery pack, and has, in addition to the transistors and resistors, two rectifying diodes and two capacitors.
It is known from the further U.S. Letters Pat. No. 3,970,912 issued on July 20, 1976 to Philip A. Hoffman and entitled "Battery Charging Circuit" to provide a battery charging circuit free of transformers and operatively arranged to produce current pulses which are supplied to the battery or batteries to be recharged via the inductance of an electric motor, which forms part of a cordless hand tool or the like.
A considerable number of battery chargers have been proposed and are known from the general prior art including U.S. Letters Patents identified as follows:
______________________________________ Numbers Patentees Issue Dates ______________________________________ 3,217,229 Lyttleton W. Ballard November 9, 1965, 3,381,639 Norman N. Potter et al. October 25, 1966, 3,563,800 Harry G. Oswin et al. February 16, 1971, 3,735,233 Richard B. Ringle May 22, 1973, 3,875,921 John H. Bigbee, III April 8, 1975, 4,013,934 George J. Frye March 22, 1977, 4,140,958 Charles R. Groeschel February 20, 1979, 4,158,813 Robert W. Ellis et al. June 19, 1979, 4,162,439 Arthur Schneider July 24, 1979, 4,186,335 Harold J. Cahill January 29, 1980, 4,220,905 William T. Quarton September 2, 1980, 4,266,178 Tatsushi Asakawa May 5, 1981, 4,292,578 Robert L. Steigerwald et al. September 29, 1981, 4,321,523 Ronald O. Hammel March 23, 1982 and 4,348,619 Ray et. al. September 7, 1982. ______________________________________
It is well known to use Zener diodes in voltage regulators to assure that voltage at a given circuit point does not exceed a given level; an example of such a circuit is disclosed in U.S. Letters Pat. No. 3,530,367 to Robert A. Gardenghi issued Sept. 22, 1970 and entitled "Zener Diode Voltage Regulator Circuit."
It is also known from Mims III "Engineer's Notebook A Handbook of Integrated Circuit Applications", First Edition, Second Printing, pg. 95, Radio Shack, A division of Tandy Corporation, U.S.A. (1970) to use integrated circuits in battery chargers.
Fabrication techniques for making semiconductor devices, including transistors and integrated circuits, and the devices themselves have become well known from a considerable number of publications. Among these publications are a book Grove, Physics and Technology of Semiconductor Devices, John Wiley and Sons, New York, New York (1967) and a book Sze, Physics of Semiconductor Devices, John Wiley and Sons, New York, New York (1969).
Active circuit parasitic transistor effects are known as phenomena, and often cause problems in integrated circuits, especially monolithic single-crystal integrated circuits, as recognized, for example, in Warner Jr. et al., Integrated Circuits Design Principles and Fabrications, pgs. 169, 204-207, McGraw-Hill Book Company, New York, New York (1965) and in Meyer et al., Analysis and Design of Integrated Circuits, pgs. 30-31, McGraw-Hill Book Company, New York, New York (1968). The conventional solution is to design the integrated circuit so that the active parasitic transistors have very low gain, are spaced at considerable distances from components with which they may interfere, are isolated from other circuit components by intrinsic zones or the like and/or remain OFF during predetermined ON times of desired circuit components.